Chandra Localization of Swift J1753.7-2544

ATel #4899; Deepto Chakrabarty (MIT), Peter G. Jonker (SRON), Craig B. Markwardt (NASA/GSFC)
on 20 Mar 2013; 17:05 UT
Credential Certification: Deepto Chakrabarty (deepto@space.mit.edu)

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As part of an ongoing Chandra program for precise localization of transient low-mass X-ray binaries, we obtained a short Chandra/ACIS-S observation of Swift J1753.7-2544 (ATels #4769, #4789, #4802, #4804, #4818). Our observation was made on 2013 March 16, 01:16 TT (MJD 56367.053), which was 51 days after the outburst onset detected by Swift/BAT (ATel #4769). Our exposure time was 970.8 s using a (1/8)-subarray of the ACIS S3 chip with 0.4 s readout time.

The source was detected with a count rate of 0.058(8) count/s. The best-fit position is

RA (J2000) = 17h 53m 39.87s
Dec (J2000) = -25d 45' 14.0"

with an error radius of 0.6 arcsec (90% containment). This position is consistent with the Swift XRT position circle (2.3 arcsec error radius, 90% confidence; ATel #4789), lying 1.2 arcsec from its center. However, our position is inconsistent with all previously reported candidate counterparts: the bright USNO/2MASS optical/IR source reported in ATel #4789 (1.1/1.4 arcsec away), the two infrared sources reported in ATel #4802 (2.6 and 3.3 arcsec away), and the ultraviolet Swift/UVOT source reported in ATel #4818 (1.9 arcsec away).

Assuming the X-ray spectrum measured by Swift/XRT (an absorbed power-law spectrum with photon index 1.3 and hydrogen column density 4.9E22 cm^(-2), ATel #4789), the absorbed (unabsorbed) 0.2-10 keV flux in our Chandra observation was 1.9E-12 (3.4E-12) erg/cm^2/s. This corresponds to an X-ray luminosity of 2.5E34 erg/s for a distance of 8 kpc.